<p>All calcualted:
<@h.img src="falcon.png" alt="Falcon" />

<p>Width calculated:
<@h.img src="falcon.png" alt="Falcon" height=20/>


<p>Height calculated:
<@h.img src="falcon.png" alt="Falcon" width=20/>

<p>Nothing calculated:
<@h.img src="falcon.png" alt="Falcon" height="20" width="20"/>
